1. Field of the Invention
This invention relates to road wheels for vehicles and more specifically to a demountable rim assembly comprising a rim to receive a tyre and an adapter band welded to the rim, the adapter band being capable of being releasably secured to a hub.
Such demountable rim assemblies are often mounted in pairs on a hub with a spacer between them as rear wheels on a vehicle or a trailer while for front wheels the rim assemblies are mounted singly on a hub. One of the problems encountered in the use of such assemblies is the lack of radial and lateral truth thereof which causes vibration and brake judder. Another problem, particularly when the assemblies are used on front wheels subject to heavy braking loads, is the need to deform the adapter band to chord it when the rim assembly is being mounted onto the hub so as to prevent relative rotational movement between the hub and adapter band during such heavy braking.
It is an object of the invention to provide demountable rim assemblies which can be used either singly or in pairs and which will perform better than those at present in use. It is also an object of the invention to provide a wheel including one or two such demountable rim assemblies.
2. SUMMARY OF THE INVENTION
According to one aspect of the invention we provide a demountable rim assembly comprising a rim and an adapter band welded to the rim, the band having an annular portion which projects from the rim centre well beyond the rim and which has internal cylindrical and divergent machined surfaces which are true about the rotary axis of the assembly having been machined after welding of the band to the rim, the free end portion of the band also having a machined free end surface which lies in a plane perpendicular to said rotary axis.
When the assembly is mounted on a hub, the cylindrical and divergent surfaces engage with complementary cylindrical and divergent surfaces on the hub. The complementary divergent surfaces are forced into frictional engagement by clamps which clamp the assembly to the hub and the cylindrical surfaces are telescoped and centre the assembly on the hub. By machining these surfaces, so that the adapter band is a close fit on the hub, radial and lateral truth of the rim is ensured and vibration and brake judder can be reduced or eliminated. By way of example, for a nominal 22.5" diameter wheel the hub may have a diameter of 18.542".+-.0.004" and the cylindrical surface in the band a diameter of 18.558".+-.0.004" giving minimum and maximum clearances between hub and band of 0.008 and 0.024" respectively.
When demountable rim assemblies embodying the invention are used in pairs, the free end surfaces of the adapter bands of the two assemblies abut to space the rims apart so that a separate spacer is not required.
According to another aspect of the invention, we provide a wheel assembly comprising a hub having an external cylindrical surface and an external divergent surface, two demountable rim assemblies mounted on the hub, each rim assembly comprising a rim and an adapter band welded to the rim, the band having an annular portion which projects from the rim centre well beyond the rim, the annular portions of the two bands being mounted about the cylindrical surface of the hub so that internal cylindrical machined surfaces on the bands engage said cylindrical surface on the hub and so that machined surfaces on free ends of the bands and lying in a plane perpendicular to the rotary axis of the wheel assembly abut, each band having an internal, machined divergent surface, the divergent surface on one of said bands engaging the divergent surface of the hub and the divergent surface on the other of said bands being engaged by clamping means so as to force said divergent surface on the one band into engagement with the divergent surface on the hub.
Thus in a dual-tyred assembly the normally used spacer can be omitted since the free ends of the adapter bands will abut. The adapter bands therefore have to be of sufficient length to space the tyres of the dual-tyred assembly.
In one embodiment of the invention the free end portion of each adapter band may be provided with notches and the demountable rim assembly may be mounted singly on a hub by clamping means which engage said free end portion and which are located in the notches to prevent relative rotation between the hub and the demountable rim assembly.
In another embodiment of the invention the adapter band has, outboardly of said divergent surface, a plurality of holes therein to receive clamping means, the free end portion of the band being continuous.
By "outboard" and "outboardly" we mean in directions away from the centre of the well of the rim.
The adapter band may have, immediately outboard of said divergent surface, a first cylindrical portion in which said internal cylindrical surface is machined and, outboardly of said first portion, a second cylindrical portion of larger diameter than said first portion, the holes intersecting both the first and second portions and the second portion providing the free end portion of the band.
By making the free end portion of the band continuous rather than slotted as in the first embodiment the adapter band is stiffer, stronger and safer .